by CNN

HONG KONG, China (CNN) -- Health officials studying how Severe Acute Respiratory Syndrome (SARS) virus is spread say they believe the disease is not transmitted in water or in the air, but could be spread by contact with a contaminated toilet seat.

But the World Health Organization believes the "major" way that SARS is spread is person-to-person contact -- for example, by speaking or coughing, a spokesman said.

On Thursday, Hong Kong's health ministry reported four more people have died from the disease bringing the total deaths there to 65. The ministry's latest SARS case count stands at 1,297 with 29 newly diagnosed patients.

Over one-quarter of the first several hundred Hong Kong cases appeared in the Amoy Gardens housing complex, causing health officials to remove residents until more was known about the disease.

Hong Kong Health Secretary Dr. Yeoh Eng-kiong said a SARS patient had visited the most affected block of that complex, Block E, on two separate occasions in March, using a toilet there.

"He might have infected other residents in Block E," Yeoh said.

The health secretary said the housing complex had been cleaned and disinfected "very thoroughly" and officials did not foresee any problems "for residents returning to their homes."

Health officials arrived at their conclusions through laboratory tests and studying outbreak patterns, Yeoh said.

Meanwhile, outgoing Hong Kong airport passengers wearing face masks were submitted to body temperature checks, part of a new proactive approach to SARS announced by the governor Wednesday.

Hong Kong Chief Executive Tung Chee Hwa said those checks will be extended to incoming passengers next week.

On Wednesday, the WHO said SARS had claimed 159 lives with 3,293 reported cases in 24 countries and territories.

The WHO also says the virus which cause SARS comes from the same group that causes the common cold but it has never before been seen in humans.

Confirming this knowledge is regarded as a key step in the hunt for a cure and possible vaccine against the disease.